Chemical instability of YBa2Cu3O7-δ at high mechanical pressures

The high-temperature superconducting phase YBa2Cu3O7−δ has been found to be unstable with respect to and decompose into other metal oxides (Y2BaCuO5, CuO, Cu2O, BaCuO2, and others) at stresses greater than 100 MPa at temperatures from 700 to 950 °C. Hot isostatic pressing and hot uniaxial pressing were used to apply pressure to and to densify porous YBa2Cu3O7−δ. X-ray diffraction and scanning electron microscopy/x-ray spectroscopy were used to determine phase purity before and after pressing. The instability of the superconducting phase should be considered during the development of hot mechanical densification and shape-forming processes, since a limit exists for the time at temperature and pressure that the YBa2Cu3O7−δ phase can withstand before decomposing.